Pollen-mediated gene flow from Kentucky bluegrass under cultivated field conditions

Kentucky bluegrass (Poa pratensis L.), one of the most commonly grown turfgrasses in temperate regions, is being developed for possible commercial release with transgenic traits. The use of this technology raises risk assessment questions because P. pratensis is perennial, often apomictic, competitive in many habitats, and hybridizes with other Poa. To further understand the potential environmental impact of a transgenic P. pratensis, we measured intra- and interspecific pollen-mediated gene flow in field conditions from P. pratensis to other Poa. We used a wagon-wheel design with a glyphosate (N-phosphono methyl-glycine) resistant P. pratensis as a pollen donor and a pollen receptor plot at 0 m and plots at 13 and 53 m along six equally spaced vectors. Each receptor plot included accessions from 25 Poa species. Seedlings from the receptor plants were screened for resistance to glyphosate and potential hybrids verified by PCR and genomic fingerprinting. Hybrids were found with P. arachnifera Torrey, P. interior Rydb., P. pratensis x P. secunda J. Presl, and three other P, pratensis entries, but did not occur with P. annua L., P. palustris L., P. trivialis L., or P. compressa L., among other species. Overall hybrid frequency was 0.048% and hybrid frequency at the 0-m distance was 0.53%. While apomixis in receptor plants and pollen competition likely reduced the number of hybrids, gene flow did occur but at low frequency and over short distances.